The Core for this Program Project provides a group of resources, services, and skills that are essential for the conduct of the component projects. These consist of: 1. Coordination and Support. Dr. Willett will coordinate and provide the overall direction for the projects conducted within this Program. The Core staff will provide administrative assistance and secretarial support for the individual projects and facilitate communications among them. 2. The Semi-Quantitative Food Frequency Questionnaire Analysis System. This questionnaire and nutrient analysis system is a basic resource that is used in all of the component studies, as well as by many other investigators within and outside our institution. The Core will support a Senior Dietitian with responsibility for maintaining and developing the food composition database used in the nutrient analysis system that accompanies the questionnaire. 3. Statistical Services. Dr. Donna Spiegelman will provide statistical support for all of the projects within this proposal. 4. Computing and Programming Facilities. The Core will provide the computer hardware and software resources for all of the component Projects. This computer facility is also coordinated with the Nurses' Health Studies I and II. A programmer included in the Core will arrange transfer of data among the component projects and other large cohort databases, and support the maintenance and development of the nutrient analysis system, and integrate the results of laboratory analyses with our existing epidemiology data for nested case-control analyses. 5. Biological Specimen Bank. Bloods, stored in aliquots of plasma, buffy coat, and red cells in liquid nitrogen freezers, are available for 18,000 participants in the Health Professionals Follow-up Study and will be used for Projects I, II, and separately funded research. The core will support the monitoring and maintenance of this valuable resource as well as specimen retrieval, aliquoting, and shipping to collaborating laboratories.